Field of the Invention
This invention relates to a coloring composition and a compound which has a high dichroic ratio. This invention further relates to an anisotropic light absorption film, a laminate, a polarizing plate and an image display device, using the coloring composition.
Background Art
For the scene where a function of attenuating, polarizing, scattering or shielding irradiated light including laser light and natural light is necessary, it has been a conventional practice to use a device which operates based on a principle differing from function to function. Products corresponded to these functions have therefore been manufactured by manufacturing processes again differing from function to function. For example, LCD (liquid crystal display) employs a linear polarizing plate or a circular polarizing plate, in order to control optical rotation or birefringence in display. The circular polarizing plate is also employed in OLED (organic light emitting diode), for the purpose of preventing reflection of external light. For these polarizing plates (polarizing elements), iodine has widely been used as a dichroic substance.
Alternatively, there has been discussed polarizing elements using organic dyes, in place of iodine, as the dichroic substance. For example, JP-A-2013-109090 describes a polarizing film composed of a composition which contains two or more species of dichroic dyes having different values of wavelength of maximum absorbance, wherein thienothiazole trisazo dye is used as the dichroic dye. JP-B2-5412225 describes an anisotropic light absorption film having a thienothiazole trisazo dye as the dichroic substance.    [PATENT DOCUMENT 1] JP-A-2013-109090    [PATENT DOCUMENT 2] JP-B2-5412225
The dichroic dyes described in JP-A-2013-109090 and JP-B2-5412225 have, how ver, been required for further improvement in dichroic ratio.